240 volt 3-wire pool pump hookup

[DKraus]

What is the correct method for hooking up a straight 240volt, 3-wire pool pump motor to a double-pole GFCI breaker. The motor has "no" neutral, only to hots and a equipment ground coming back to main breaker panel. Can the GFCI operate correctly without a load neutral connected to it.?

 

[augie47]

The GFCI will need to be connected to the line neutral to function properly but there need be nothing connected to the "load neutral" terminal.

 

[Volta]

Welcome to (posting on) the forum!


As Augie said, no neutral load is need on the GFCI, for either Code or operational reasons.

 

[DKraus]

Thanks for the Help.

 

[bullheimer]

I AM BUMPING THIS Q BECAUSE I WANT SOMEBODY TO EXPLAIN HOW IN THE HL THIS GFI BREAKER IS GONNA WORK W/O A LOAD NEUT.

my text book says that a gfi "monitors the current of the hot and the neutral wires (talking about a 120V gfi) comparing them, and if it senses a difference of 3-5 mA, trips)

so i don't see any way that it will ever trip. ANYBODY please, clue me in! my hot tub says "must have gfi protection" for their 3 wire ckt. At $140 for ONE C-H type ch breaker i am pretty much p-o'd at having to put this in.

 

[mxslick]

I AM BUMPING THIS Q BECAUSE I WANT SOMEBODY TO EXPLAIN HOW IN THE HL THIS GFI BREAKER IS GONNA WORK W/O A LOAD NEUT.

my text book says that a gfi "monitors the current of the hot and the neutral wires (talking about a 120V gfi) comparing them, and if it senses a difference of 3-5 mA, trips)

so i don't see any way that it will ever trip. ANYBODY please, clue me in! my hot tub says "must have gfi protection" for their 3 wire ckt. At $140 for ONE C-H type ch breaker i am pretty much p-o'd at having to put this in.

It's easy. Since a 240v circuit has the current "going out one hot and returning to the other" the two hots are monitored and any difference in the current between the two (just as any difference in current flow from hot to the neutral on a 120v GFCI) will trigger the trip circuits.

AFAIK the neutral lead and load terminal are strictly there to accommodate loads that require them. The neutral line side probably has to be connected to power the gfci circuitry though.

 

[hurk27]

Basically the current carrying conductors all pass through a donut type coil, this coil will not develop any current since current going out on one conductor returns through the same coil on one of the other conductors, this includes the neutral, it doesn't matter if the neutral has current on it or not , but just that the current going out to the load on one conductor returns on the other through the same coil, if the neutral was being used, then current going out on one hot lets say 10 amps, and 3 amps returned on the other hot, and 7 amps returned on the neutral, the GFCI would not trip, but if the neutral instead had 6.995 amp returning then it will, when current is formed on this coil (current transformer as its called) if it reaches the equivalent of 5 ma's the electronics in the breaker will open the circuit (which needs 120 volts to operate) so the reason for the pigtail to be required to be hooked up, some do have 240 volt electronics in it, but the pigtail is still required for the test button to work.

 

[busman]

Try thinking about it this way. There is a load neutral wire - it's just very, very, very short and not connected to anything. No difference to a balanced load with a connected neutral, but the neutral current is zero.

Mark

 

[Dennis Alwon]

It gets more complicated in my eyes, when you have a 240v gfci, say for a hot tub, that enlists a neutral. How does the 50 DP gfci know whether the load is 240 or 120. Thus you may have a 240v motor and a 120v light. Obviously the current will be different one one phase. It seems that the device can monitor this somehow.

Anybody know????

 

[winnie]

hurk27 described how it works above.

You have a single 'current transformer', and _all_ of the circuit conductors pass through the window of this current transformer.

As long as any current going out on each of the conductor is balanced by current returning on the other conductors, the _net_ current of the entire bundle is zero. You don't need to do any fancy math; the physics of the situation is that if all of the current flow is balanced among the total set of wires, then the net current in the set of wires is zero.

If current is 'leaking' somewhere out of the intended circuit conductors, then the current transformer will measure that leakage, as current going out on one wire that is not balanced by current flowing somewhere on the other set of wires. If you want to detect a ground fault, you simply need to look for net current on the entire set of wires.

-Jon

 

[LarryFine]

I AM BUMPING THIS Q BECAUSE I WANT SOMEBODY TO EXPLAIN HOW IN THE HL THIS GFI BREAKER IS GONNA WORK W/O A LOAD NEUT.

my text book says that a gfi "monitors the current of the hot and the neutral wires (talking about a 120V gfi) comparing them, and if it senses a difference of 3-5 mA, trips)

It gets more complicated in my eyes, when you have a 240v gfci, say for a hot tub, that enlists a neutral. How does the 50 DP gfci know whether the load is 240 or 120. Thus you may have a 240v motor and a 120v light. Obviously the current will be different one one phase. It seems that the device can monitor this somehow.

Anybody know????

The GFCI doesn't "need to know" whether there's a grounded circuit conductor, whether there's one or two hots, or anything else. The only 'requirement' is that the system is grounded, as compared to a floating (non-bonded) source.

With apologies to the previous posts, I'm goint to start from scratch:

A GFCI device works by comparing the total current, algebraically speaking, through all of a circuit's conductors. If all of the current being supplied through any conductor is being matched, or returned, through the other conductor(s), the net total current is zero.

This is accomplished by passing all of the circuit conductors through a ferrous ring which has a small coil wrapped aorung one side. As long as all of the currents match, no magnetism is developed in the ring, and no voltage is developed in the small coil.

Added: This is basically the same theory as why we want conductors of every phase in a metallic conduit: so the net current will be zero and not heat the conduit. The currents of each wire need not match for this to work, only that the total algebraically adds to zero.

If someone is getting a shock, that means that the current flowing through their body is flowing from the source, through one hot wire, but is returning to the source through a pathway other than another wire, meaning through the earth or another grounded, conductive surface.

The difference in conductor currents means there is now a sum of other than zero current, which creates a magnetism in the ring and a voltage in the small coil, which is amplified, and trips the GFCI mechanism when the detected current exceeds about 5 milliamps (5/1000 of an amp).

So, the very practice which makes the GFCI necessary, grounding one conductor of our supply, is also necessary for it to function. Whether there is one or more hot wires, or whether the grounded conductor is required by the load, don't matter. It only matters that some current is getting around the ring.

Note that someone getting shocked between two circuit conductors, again regardless of whether it's line-to-line or line-to-neutral, will not be protected, because all of the shocking current is passing through the ring, and appears to be normal current.

So, the GFCI doesn't compare hot-to-neutral, per se, but wire to wire (to wire). They could make a 3-phase GFCI, but I don't know if there is one. There are also GFCI devices that have the ring exposed, and you pass your own wires through the ring when you install it.

Hope that was helpful.

 

[iwire]

If the current going out does not match the current comming in the GFCI will trip.

I like simple answers.

 

[LarryFine]

I like simple answers.

Me, too, but the questioners didn't seem to be satisfied with them.

 

[iwire]

Me, too, but the questioners didn't seem to be satisfied with them.

I don't know what you mean but now we have both, the simple and the long.

 

[LarryFine]

I don't know what you mean . . .

I mean:

I AM BUMPING THIS Q BECAUSE I WANT SOMEBODY TO EXPLAIN HOW IN THE HL THIS GFI BREAKER IS GONNA WORK W/O A LOAD NEUT.

my text book says that a gfi "monitors the current of the hot and the neutral wires (talking about a 120V gfi) comparing them, and if it senses a difference of 3-5 mA, trips)

so i don't see any way that it will ever trip. ANYBODY please, clue me in! my hot tub says "must have gfi protection" for their 3 wire ckt. At $140 for ONE C-H type ch breaker i am pretty much p-o'd at having to put this in.

. . . and:

It gets more complicated in my eyes, when you have a 240v gfci, say for a hot tub, that enlists a neutral. How does the 50 DP gfci know whether the load is 240 or 120. Thus you may have a 240v motor and a 120v light. Obviously the current will be different one one phase. It seems that the device can monitor this somehow.

Anybody know????

So, I elaborated.



"And, now you know . . . the r-r-r-r-r-r-rest of the story!" ~ Paul Harvey Aurandt

 

[jim dungar]

I believe confusion comes when people try to provide partially simplified answers.

Take the phrase a GFCI "compares the current in the hot wire to the current in the neutral". This partial simple explanation often leads to the assumption that a neutral is required.

A true simplified answer would be a GFCI "compares the currents in all of the wires" or even a GFCI "compares what goes out to what comes back". Of course, we need to add that all GFCI's include a line side neutral for their test button to work.

 

[bullheimer]

okay, well then!
thanks to all the above, and jim if you want to slap somebody, hit Mullins.